EP3609989A1

EP3609989A1 - Lubricant composition, in particular for limiting friction

Info

Publication number: EP3609989A1
Application number: EP18721697.3A
Authority: EP
Inventors: Benoit Thiebaut; Pushkar DESHPANDE; Fabrice DASSENOY; Clotilde MINFRAY
Original assignee: Centre National de la Recherche Scientifique CNRS; Ecole Centrale de Lyon; Total Marketing Services SA
Current assignee: Centre National de la Recherche Scientifique CNRS; Ecole Centrale de Lyon; TotalEnergies Onetech SAS
Priority date: 2017-04-11
Filing date: 2018-04-11
Publication date: 2020-02-19
Anticipated expiration: 2038-04-11
Also published as: CN110869477B; CN110869477A; WO2018189223A1; FR3065007B1; FR3065007A1; EP3609989B8; EP3609989B1; US20200102522A1

Abstract

The invention concerns a lubricant composition comprising: at least one base oil; 0.05 to 1.5% by weight of an organomolybdenum compound; and 0.005 to 1% by weight of TiO₂ particles.

Description

Lubricating composition in particular to limit friction

The present application relates to new lubricating compositions, in particular for an internal combustion engine, in particular a vehicle engine, in particular a motor vehicle. In a particularly preferred manner, the present invention relates to lubricating compositions for reducing friction between parts.

It is known to use, in lubricating compositions, molybdenum-based compounds as a friction modifier, especially organomolybdenum compounds. These organomolybdenum compounds form by tribochemical decomposition, in the presence of iron, in the contacts during the friction, MoS ₂ which makes it possible to limit the friction between the parts. However, during this tribochemical decomposition, a part of the organomolybdenum compounds is converted into molybdenum oxide and molybdenum oxysulphide which have no effect on the limitation of friction. It is therefore generally necessary to use large quantities of organomolybdenum compounds (to optimize the amount of MoS ₂ produced) in the lubricant compositions which can have adverse effects on the lubricated parts, in particular corrosion, fouling, and deterioration of the coatings in the case of carbon-coated parts.

It is known, in particular from CN104450069, lubricating compositions comprising MoS ₂ and titanium particles, in particular TiO ₂ , to make it possible to reduce the friction and wear of parts.

It is also known, in particular from US5709936, coating of parts comprising titanium, in particular titanium carbide or nitride and / or molybdenum to reduce friction.

It is also known from WO201 1 12372 lubricating compositions comprising organomolybdenum compounds and liposoluble titanium compounds.

There is an interest in providing lubricating compositions that reduce the friction between the parts and also reduce the wear of these parts. There is also an interest in providing lubricating compositions for reducing the amount of molybdenum compound introduced.

An object of the present application is to provide lubricating compositions for reducing friction between parts.

An object of the present application is also to provide such lubricating compositions also to reduce wear of parts. An object of the present application is still to provide such compositions allowing a duration of anti-friction action over a longer period.

Another object of the present application is also to provide a lubricating composition comprising a molybdenum compound reducing content.

Still other objects will appear on reading the description of the invention which follows.

These objectives are fulfilled by the present invention which provides a lubricant composition comprising:

at least one base oil;

from 0.05 to 1.5% by weight of an organomolybdenum compound; and

from 0.005 to 1% by weight of TiO ₂ particles.

In the context of the present invention, the term "organomolybdenum compound" is intended to mean compounds comprising molybdenum and an organic part, that is to say a part comprising carbon atoms. It should therefore be understood that molybdenum disulfide (MoS ₂ ) is not an organomolybdenum compound according to the invention.

Preferably, the TiO ₂ particles have a mean size of between 10 nm and 1 μm, preferably between 10 nm and 500 nm, more preferably between 10 nm and 250 nm, and even more preferably between 10 nm and 150 nm. In the context of the present invention, mean particle size means the average particle diameter. This average diameter can be measured by any method known to those skilled in the art such as, for example, counting by optical or electronic microscopy, measurement by light scattering or by laser diffraction. The light scattering measurement may in particular be carried out using a Malvern zetasizer (so-called "Dynamic Light Scattering" technique, the laser diffraction measurement can be made with a Malvern Mastersizer device.

Particles TiO ₂ may especially come from rutile or anatase. Preferably, the composition according to the invention comprises from 0.08 to 1% by weight of organomolybdenum compound relative to the total weight of the lubricating composition.

Preferably, the composition according to the invention comprises from 0.01 to 0.8% by weight of TiO ₂ particles relative to the total weight of the lubricant composition. Advantageously, the addition to the lubricant composition of TiO ₂ particles makes it possible to reduce the amount of organomolybdenum compound normally used to limit friction. Indeed, without wishing to be bound by any theory, the inventors have, surprisingly, shown that the mixture of organomolybdenum compound and TiO ₂ particles advantageously allowed to have an excellent conversion rate of the organomolybdenum compound to MoS ₂ avoiding the generation of molybdenum oxysulfide in the lubricating composition and thus the loss of active molybdenum to prevent friction. This specific combination of organomolybdenum and titanium particles according to the invention therefore makes it possible to considerably reduce friction at a lower content of organomolybdenum compound.

By organomolybdenum compound according to the invention is meant any organomolybdenum compound soluble in an oil, especially in a base oil.

The organomolybdenum compound according to the present invention may be chosen from organic complexes of molybdenum comprising at least one molybdenum (Mo) chemical element and at least one ligand such as a carboxylate ligand, an ester ligand, an amide ligand or a dithiophosphate ligand. or a dithiocarbamate ligand.

For example, organic complexes of molybdenum with carboxylates, esters, amides can be obtained by reacting molybdenum oxide or ammonium molybdates with fatty substances, glycerides, fatty acids or fatty acid derivatives (esters , amines, amides, ...).

For the purpose of the invention, the carboxylate ligands, the ester ligands and the amide ligands are free of sulfur and phosphorus.

In one embodiment, the organomolybdenum compound of the invention is selected from molybdenum complexes with amide ligands, mainly prepared by reaction of a molybdenum source, which may be for example molybdenum trioxide, and a derivative of amine, and of fatty acids comprising, for example, from 4 to 36 carbon atoms, such as, for example, the fatty acids contained in vegetable or animal oils.

The synthesis of such compounds is for example described in patents US4889647, EP0546357, US5412130 or EP1770153.

In a preferred embodiment of the invention, the organomolybdenum compound is chosen from organic complexes of molybdenum with amide ligands obtained by reaction:

(i) a mono, di or tri glyceride fatty substance, or fatty acid, (ii) an amino source of formula (A)

in which :

X ¹ represents an oxygen atom or a nitrogen atom,

X ² represents an oxygen atom or a nitrogen atom,

n or m represents 1 when X ¹ or X ^{2 respectively} represents an oxygen atom,

n or m represents 2 when X ¹ or X ^{2 respectively} represents a nitrogen atom,

(iii) and a molybdenum source selected from molybdenum trioxide or molybdates, preferably ammonium molybdate.

Advantageously, the molybdenum source is used in an amount sufficient to provide 0.1 to 30 mol% of molybdenum relative to the total weight of the molybdenum organic complex with amide ligands, more preferably from 0.1 to 20.0% of molybdenum. molybdenum.

In one embodiment of the invention, the organomolybdenum compound may comprise from 2 to 8.5% by weight of molybdenum relative to the total weight of the organic molybdenum complex with amide ligands.

Preferably, the organomolybdenum compound comprises at least one organic complex of molybdenum of formula (III) or (IV), alone or as a mixture:

in which :

X ¹ represents an oxygen atom or a nitrogen atom;

X ² represents an oxygen atom or a nitrogen atom;

n represents 1 when X ¹ represents an oxygen atom and m represents 1 when represents an oxygen atom; n represents 2 when X ¹ represents a nitrogen atom and m represents 2 when X ² represents a nitrogen atom;

R 1 represents a linear or branched, saturated or unsaturated alkyl group comprising from 4 to 36 carbon atoms, preferentially from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon atoms;

in which :

X ¹ represents an oxygen atom or a nitrogen atom;

X ² represents an oxygen atom or a nitrogen atom;

n represents 1 when X ¹ represents an oxygen atom and m represents 1 when X ² represents an oxygen atom;

n represents 2 when X ¹ represents a nitrogen atom and m represents 2 when X ² represents a nitrogen atom;

R _i represents a linear or branched alkyl group, saturated or unsaturated, comprising from 4 to 36 carbon atoms, preferably from 4 to 20 carbon atoms, preferably from 6 to 18 carbon atoms;

R ₂ represents a linear or branched, saturated or unsaturated alkyl group comprising from 4 to 36 carbon atoms, preferentially from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon atoms.

Advantageously, the organic complex of molybdenum of formula (I I I) or (IV) is prepared by reaction:

(i) a mono, di or tri glyceride fatty substance, or fatty acid,

(ii) diethanolamine or 2- (2-aminoethyl) aminoethanol,

(iii) and a molybdenum source selected from molybdenum trioxide or molybdates, preferably ammonium molybdate. More preferably, the molybdenum organic complex of formula (I II) is composed of at least one compound of formula (IIIa) or (IIb), alone or as a mixture:

in which R 1 represents a linear or branched, saturated or unsaturated alkyl group comprising from 4 to 36 carbon atoms, preferentially from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon atoms,

in which R 1 represents a linear or branched, saturated or unsaturated alkyl group comprising from 4 to 36 carbon atoms, preferably from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon atoms.

As examples of sulfur-free molybdenum complexes according to the invention, mention may be made of Molyvan 855® sold by the company Vanderbilt.

In another embodiment of the invention, the organomolybdenum compound is selected from organic complexes of molybdenum with dithiophosphate ligands or organic complexes of molybdenum with dithiocarbamate ligands.

Within the meaning of the invention, organic complexes of molybdenum with dithiophosphate ligands are also called molybdenum dithiophosphates or Mo-DTP compounds and organic complexes of molybdenum with dithiocarbamate ligands are also called molybdenum dithiocarbamates or Mo-DTC compounds .

In a more preferred embodiment of the invention, the organomolybdenum compound is selected from molybdenum dithiocarbamates.

Mo-DTC compounds are complexes formed of a metal core of molybdenum bound to one or more ligands, the ligand being an alkyl dithiocarbamate group. These compounds are well known to those skilled in the art. In one embodiment of the invention, the Mo-DTC compound may comprise from 1 to 40%, preferably from 2 to 30%, more preferably from 3 to 28%, advantageously from 4 to 15% by weight of molybdenum, relative to the total weight of Mo-DTC compound. In another embodiment of the invention, the Mo-DTC compound may comprise from 1 to 40%, preferably from 2 to 30%, more preferably from 3 to 28%, advantageously from 4 to 15% by weight of sulfur. , based on the total weight of Mo-DTC compound. In another embodiment of the invention, the Mo-DTC compound may be chosen from those whose nucleus has two molybdenum atoms (also called dimeric Mo-DTC) and those whose nucleus has three molybdenum atoms (also called Trimeric Mo-DTP). In another embodiment of the invention, the trimeric Mo-DTC compounds have the formula Mo ₃ S _k L _n wherein:

k represents an integer at least equal to 4, preferably ranging from 4 to 10, advantageously from 4 to 7,

n is an integer ranging from 1 to 4, and

L being an alkyl dithiocarbamate group comprising from 1 to 100 carbon atoms, preferably from 1 to 40 carbon atoms, preferably from 3 to 20 carbon atoms.

Examples of trimeric Mo-DTC compounds according to the invention include the compounds and methods for their preparation as described in WO 98/26030 and US 2003/022954.

In a preferred embodiment of the invention, the Mo-DTC compound is a dimeric Mo-DTC compound.

As examples of dimeric Mo-DTC compounds, mention may be made of the compounds and their methods of preparation as described in the documents EP 0757093, EP15 0719851, EP 0743354 or EP 1013749.

The dimeric Mo-DTC compounds generally correspond to the compounds of formula (V):

in which :

R3, _R4, R5, Re, identical or different, represent independently a hydrocarbon group selected from alkyl, alkenyl, aryl, cycloalkyl or cycloalkenyl,

X ₃ , X ₄ , X ₅ and X ₆ , which may be identical or different, independently represent an oxygen atom or a sulfur atom.

For the purposes of the invention, the term "alkyl group" means a linear or branched, saturated or unsaturated hydrocarbon-based group comprising from 1 to 24 carbon atoms, preferably from 4 to 18 carbon atoms.

In one embodiment of the invention, the alkyl group is selected from the group consisting of methyl, ethyl, propyl, isopropyl, n-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, isotridecyl, tetradecyl, hexadecyl, stearyl, icosyl, docosyl, tetracosyl, triacontyl, 2-ethylhexyl, 2-butyloctyl, 2-butyldecyl, 2-hexyloctyl, 2-hexyldecyl, 2-octyldecyl, 2-hexyldodecyl , 2-octyldodecyl, 2-decyltetradecyl, 2-dodecylhexadecyl, 2-hexadecyloctadecyl, 2-tetradecyloctadecyl, myristyl, palmityl and stearyl.

For the purposes of the present invention, the term "alkenyl group" means a linear or branched hydrocarbon group comprising at least one double bond and comprising from 2 to 24 carbon atoms. The alkenyl group may be chosen from vinyl, allyl, propenyl, butenyl, isobutenyl, pentenyl, isopentenyl, hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tetradecenyl and oleic.

Aryl group within the meaning of the present invention means a polycyclic aromatic hydrocarbon or an aromatic group, substituted or not with an alkyl group. The aryl group may comprise from 6 to 24 carbon atoms.

In one embodiment, the aryl group may be selected from the group consisting of phenyl, toluyl, xylyl, cumenyl, mesityl, benzyl, phenethyl, styryl, cinnamyl, benzhydryl, trityl, ethylphenyl, propylphenyl, butylphenyl, pentylphenyl, hexylphenyl, heptylphenyl, octylphenyl, nonylphenyl, decylphenyl, undecylphenyl, dodecylphenyl, phenylphenyl, benzylphenyl, phenylstyrene, p-cumylphenyl and naphthyl.

By cycloalkyl group within the meaning of the present invention is meant a polycyclic or cyclic hydrocarbon, substituted or not with an alkyl group.

By cycloalkenyl group within the meaning of the present invention is meant a polycyclic or cyclic hydrocarbon, substituted or not with an alkyl group, and comprising at least one unsaturation.

Cycloalkyl groups and cycloalkenyl groups may comprise from 3 to 24 carbon atoms.

For the purpose of the present invention, the cycloalkyl groups and the cycloalkenyl groups may be chosen, in a non-limiting manner, from the group consisting of cyclopentyl, cyclohexyl, cycloheptyl, methylcyclopentyl, methylcyclohexyl, methylcycloheptyl, cyclopentenyl, cyclohexenyl, cycloheptenyl, methylcyclopentenyl, methylcyclohexenyl.

In a preferred embodiment of the invention, R ₃ , R ₄ , R ₅ and R ₆ , which may be identical or different, independently represent an alkyl group comprising from 1 to 24 carbon atoms, preferably from 4 to 18 carbon atoms. or an alkenyl group comprising from 2 to 24 carbon atoms.

In one embodiment of the invention, X ₃ , X ₄ , X ₅ and X ₆ may be identical and may represent a sulfur atom. In another embodiment of the invention, X ₃ , X ₄ , X ₅ and X ₆ may be the same and may be an oxygen atom.

In another embodiment of the invention, X ₃ and X ₄ may represent a sulfur atom and X ₅ and X ₆ may represent an oxygen atom.

In another embodiment of the invention, X ₃ and X ₄ may represent an oxygen atom and X ₅ and X ₆ may represent a sulfur atom.

In another embodiment of the invention; the ratio in number of sulfur atoms relative to the number of oxygen atoms (S / O) of the compound Mo-DTC may vary from (1/3) to (3/1). In another embodiment of the invention, the Mo-DTC compound of formula (V) may be chosen from a symmetrical Mo-DTC compound, an asymmetric Mo-DTC compound and their combination.

By symmetric Mo-DTC compound according to the invention is meant a Mo-DTC compound of formula (V) in which the groups R ₃ , R ₄ , R ₅ and R ₆ are identical.

By asymmetric Mo-DTC compound according to the invention is meant a Mo-DTC compound of formula (V) in which the groups R ₃ and R ₄ are identical, the groups R ₅ and R ₆ are identical and the groups R ₃ and R ₄ are different from the groups R ₅ and R ₆ .

In a preferred embodiment of the invention, the Mo-DTC compound is a mixture of at least one symmetrical Mo-DTC compound and at least one asymmetric Mo-DTC compound.

In one embodiment of the invention, R ₃ and R ₄ , which are identical, represent an alkyl group comprising from 5 to 15 carbon atoms, preferably from 8 to 13 carbon atoms, and R ₅ and R ₆ , which are identical, represent an alkyl group comprising from 5 to 15 carbon atoms, preferably from 8 to 13 carbon atoms, and the groups R ₃ and R ₄ are identical or different from the groups R ₅ and R ₆ .

In another preferred embodiment of the invention, R ₃ and R ₄ , which are identical, represent an alkyl group comprising from 6 to 10 carbon atoms and R ₅ and R ₆ , which are identical, represent an alkyl group comprising from 10 to 15 carbon atoms. carbon atoms, and the groups R ₃ and R ₄ are different from the groups R ₅ and R ₆ .

In another preferred embodiment of the invention, R ₃ and R ₄ , which are identical, represent an alkyl group comprising from 10 to 15 carbon atoms and R ₅ and R ₆ , which are identical, represent an alkyl group comprising from 6 to 10 carbon atoms. carbon atoms, and the groups R ₃ and R ₄ are different from the groups R ₅ and R ₆ .

In another preferred embodiment of the invention, R ₃ , R ₄ , R ₅ and R ₆ , which are identical, represent an alkyl group comprising from 5 to 15 carbon atoms, preferably from 8 to 13 carbon atoms. Advantageously, the compound Mo-DTC is chosen from compounds of formula (V) in which:

X ₃ and X ₄ represent an oxygen atom,

X ₅ and X ₆ represent a sulfur atom,

R ₃ represents an alkyl group comprising 8 carbon atoms or an alkyl group comprising 13 carbon atoms,

R ₄ represents an alkyl group comprising 8 carbon atoms or an alkyl group comprising 13 carbon atoms,

- R ₅ represents an alkyl group comprising 8 carbon atoms or an alkyl group comprising 13 carbon atoms,

- R ₆ represents an alkyl group comprising 8 carbon atoms or an alkyl group comprising 13 carbon atoms.

Thus, advantageously, the compound Mo-DTC is chosen from the compounds of

(Goes)

wherein the groups R ₃ , R ₄ , R ₅ and R ₆ are as defined for formula (V).

More advantageously, the compound Mo-DTC is a mixture:

a Mo-DTC compound of formula (Va) in which R ₃ , R ₄ , R ₅ and R ₆ represent an alkyl group comprising 8 carbon atoms,

- a Mo-DTC compound of formula (Va) wherein R _3, R _4, R 5 and R ₆ represent an alkyl group containing 13 carbon atoms, and / or

a Mo-DTC compound of formula (Va) in which R ₃ , R ₄ represent an alkyl group comprising 8 carbon atoms and R ₅ and R ₆ represent an alkyl group comprising 13 carbon atoms.

Examples of Mo-DTC compounds that may be mentioned are Molyvan L®, Molyvan 807® or Molyvan 822® products marketed by RT Vanderbilt Compagny® or Sakura-lube 200®, Sakura-lube 165® and Sakura-lube products. 525® or Sakura-lube 600® marketed by the company Adeka. The lubricant composition according to the invention may further comprise at least one anti-wear additive chosen from phospho-sulfur-containing additives such as metal alkylthiophosphates, in particular zinc alkylthiophosphates, and more specifically zinc dialkyldithiophosphates.

In general, the lubricating composition according to the invention may comprise any type of mineral lubricating base oil, synthetic or natural, animal or vegetable, known to those skilled in the art.

The base oils used in the lubricant compositions according to the invention may be oils of mineral or synthetic origins belonging to groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification) (Table A) or their mixtures.

Table A The mineral base oils according to the invention include all types of base oils obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as solvent extraction, desalting, solvent dewaxing, hydrotreating , hydrocracking, hydroisomerization and hydrofinishing.

Mixtures of synthetic and mineral oils can also be used.

There is generally no limitation on the use of different lubricating bases for producing the lubricating compositions according to the invention, except that they must have properties, in particular viscosity, viscosity index, sulfur content. , oxidation resistance, suitable for use for engines or for vehicle transmissions. The base oils of the lubricating compositions according to the invention may also be chosen from synthetic oils, such as certain carboxylic acid esters and alcohols, and from polyalphaolefins. The polyalphaolefins used as base oils are, for example, obtained from monomers comprising from 4 to 32 carbon atoms, for example from octene or decene, and whose viscosity at 100 ° C. is between 1, 5 and 15 mm ² . s ^"1 according to the ASTM D445 standard. Their average molecular weight is generally between 250 and 3000 according to the ASTM D5296 standard. Preferably, the base oils of the present invention are selected from the above base oils which the aromatic content is between 0 and 45%, preferably between 0 and 30% The aromatic content of the oils is measured according to the Burdett UV method Without being bound by any theory, the aromaticity of the oil The choice of an oil low in aromatics allows an optimum at a higher temperature.

Advantageously, the lubricant composition according to the invention comprises at least 50% by weight of base oils relative to the total mass of the composition.

More advantageously, the lubricating composition according to the invention comprises at least 60% by weight, or even at least 70% by weight, of base oils relative to the total mass of the composition.

More particularly advantageously, the lubricant composition according to the invention comprises from 60 to 99.5% by weight of base oils, preferably from 70 to 99.5% by weight of base oils, relative to total mass of the composition.

Many additional additives can be used for this lubricating composition according to the invention.

The additional additives that are preferred for the lubricating composition according to the invention are chosen from detergent additives, the anti-wear additives different from the phospho-sulfur additives, the friction modifying additives different from the organomolybdenum compounds, the extreme pressure additives, the dispersants, the pour point improvers, defoamers, thickeners and mixtures thereof. Amine phosphates are anti-wear additives that can be used in the lubricating composition according to the invention. However, the phosphorus brought by these additives can act as poison catalytic systems of automobiles because these additives are ash generators. These effects can be minimized by partially substituting amine phosphates with non-phosphorus additives, such as, for example, polysulfides, especially sulfur-containing olefins.

Advantageously, the lubricant composition according to the invention may comprise from 0.01 to 6% by weight, preferably from 0.05 to 4% by weight, more preferably from 0.1 to 2% by weight relative to the mass. total lubricating composition, anti-wear additives and extreme pressure additives.

Advantageously, the lubricant composition according to the invention may comprise at least one additional friction modifier additive different from the organomolybdenum compounds. The additional friction modifier additive may be selected from a compound providing metal elements and an ash free compound. Among the compounds providing metal elements, mention may be made of transition metal complexes such as Sb, Sn, Fe, Cu, Zn, the ligands of which may be hydrocarbon compounds comprising oxygen, nitrogen, sulfur or of phosphorus. The ashless friction modifier additives are generally of organic origin and may be selected from monoesters of fatty acids and polyols, fatty epoxides, borate fatty epoxides; or glycerol esters of fatty acid. According to the invention, the fatty compounds comprise at least one hydrocarbon group comprising from 10 to 24 carbon atoms.

Advantageously, the lubricant composition according to the invention may comprise at least one antioxidant additive.

The antioxidant additive generally serves to retard the degradation of the lubricating composition in service. This degradation can notably result in the formation of deposits, the presence of sludge or an increase in the viscosity of the lubricant composition.

Antioxidant additives act in particular as radical inhibitors or destroyers of hydroperoxides. Among the antioxidant additives commonly used, mention may be made of antioxidant additives of phenolic type, antioxidant additives of amine type, antioxidant phosphosulfur additives. Some of these antioxidant additives, for example phosphosulfur antioxidant additives, can be ash generators. Phenolic antioxidant additives may be ash-free or may be in the form of neutral or basic metal salts. Antioxidant additives may especially be chosen from sterically hindered phenols, sterically hindered phenol esters and sterically hindered phenols comprising a thioether bridge, diphenylamines, diphenylamines substituted by at least one C ₁ -C ₁₂ alkyl group, Ν, Ν ' dialkyl-aryl diamines and mixtures thereof.

Preferably, according to the invention, the sterically hindered phenols are chosen from compounds comprising a phenol group in which at least one vicinal carbon of the carbon carrying the alcohol function is substituted by at least one alkyl group in the form of d-C ₁₀ , preferably a grouping. C ₁ -C ₆ alkyl, preferably a C ₄ alkyl group, preferably by the ter-butyl group.

Amino compounds are another class of antioxidant additives that can be used, optionally in combination with phenolic antioxidant additives. Examples of amine compounds are aromatic amines, for example aromatic amines of formula NR ⁷ R ⁸ R ⁹ in which R ⁷ represents an optionally substituted aliphatic or aromatic group, R ⁸ represents an optionally substituted aromatic group, R ⁹ represents a hydrogen atom, an alkyl group, an aryl group or a group of formula R ¹⁰ S (O) _z R ¹¹ in which R ¹⁰ represents an alkylene group or an alkenylene group, R ¹¹ represents an alkyl group, a alkenyl group or an aryl group and z represents 0, 1 or 2.

Sulfurized alkyl phenols or their alkali and alkaline earth metal salts can also be used as antioxidant additives.

Another class of antioxidant additives is copper compounds, for example copper thio- or dithio-phosphates, copper and carboxylic acid salts, dithiocarbamates, sulphonates, phenates, copper acetylacetonates. Copper salts I and II, succinic acid or anhydride salts can also be used.

The lubricant composition according to the invention may contain all types of antioxidant additives known to those skilled in the art.

Advantageously, the lubricating composition comprises at least one ash-free antioxidant additive.

Also advantageously, the lubricating composition according to the invention comprises from 0.5 to 2% by weight relative to the total weight of the composition, of at least one antioxidant additive. The lubricant composition according to the invention may also comprise at least one detergent additive.

The detergent additives generally make it possible to reduce the formation of deposits on the surface of the metal parts by dissolving the secondary oxidation and combustion products.

The detergent additives that can be used in the lubricant composition according to the invention are generally known to those skilled in the art. The detergent additives may be anionic compounds comprising a long lipophilic hydrocarbon chain and a hydrophilic head. The associated cation may be a metal cation of an alkali metal or alkaline earth metal.

The detergent additives are preferably chosen from the alkali metal or alkaline earth metal salts of carboxylic acids, the sulphonates, the salicylates, the naphthenates and the phenate salts. The alkali and alkaline earth metals are preferably calcium, magnesium, sodium or barium.

These metal salts generally comprise the metal in stoichiometric amount or in excess, therefore in an amount greater than the stoichiometric amount. It is then overbased detergent additives; the excess metal bringing the overbased character to the detergent additive is then generally in the form of an oil insoluble metal salt, for example a carbonate, a hydroxide, an oxalate, an acetate, a glutamate, preferably a carbonate .

Advantageously, the lubricant composition according to the invention may comprise from 2 to 4% by weight of detergent additive relative to the total mass of the lubricating composition. Also advantageously, the lubricant composition according to the invention may also comprise at least one pour point depressant additive.

By slowing the formation of paraffin crystals, pour point depressant additives generally improve the cold behavior of the lubricant composition according to the invention.

As examples of pour point depressant additives, mention may be made of alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalenes and alkylated polystyrenes.

Advantageously, the lubricant composition according to the invention may also comprise at least one dispersing agent. The dispersing agent may be chosen from Mannich bases, succinimides and their derivatives.

Also advantageously, the lubricating composition according to the invention may comprise from 0.2 to 10% by weight of dispersing agent relative to the total mass of the lubricating composition.

The lubricating composition of the present invention may also comprise at least one additional viscosity index improving polymer. As examples of additional viscosity index improving polymers, there may be mentioned polymeric esters, homopolymers or copolymers, hydrogenated or non-hydrogenated, styrene, butadiene and isoprene, polymethacrylates (PMA).

The present invention also relates to the use of the lubricant composition as defined above for engine lubrication, in particular an internal combustion engine, for example a vehicle engine.

Advantageously, the lubricant composition according to the invention makes it possible to reduce friction, in particular between two parts of an engine, in particular an internal combustion engine, for example a vehicle engine.

Thus, the invention relates to the use of the lubricant composition according to the invention for reducing wear on the parts of an engine, for example a vehicle engine.

The present application also relates to a method of lubricating mechanical parts, in particular in an engine, in particular an internal combustion engine, comprising at least one step of contacting at least one part with a lubricating composition according to the invention.

The present invention will now be described by way of non-limiting examples.

FIG. 1 represents the X-ray photoelectron spectrum (the spectrum gives the binding energies (eV)) produced on the lubricant films (from compositions according to the invention) obtained at the end of tribological tests on steel / steel parts. . Example 1: Lubricating compositions

The compositions of Table 1 (CL: lubricating composition according to the invention, CC: comparative composition) were prepared by mixing the TiO ₂ particles and the organomolybdenum compound in a base oil at 60 ° C. to obtain a good dispersion of the particles. in the composition.

Example 2: Results of the tribological tests

2.1 Tests on alternating ball-plane tribometer Measurements of the coefficient of friction and the wear of the balls in μηι in diameter of the impression of the ball (table 2) were carried out on an alternating tribometer ball-plane. These tests were performed by changing for each test the mechanical parts of flat surface. The parts used are as follows:

the balls have a diameter of 5 mm and are mechanical parts made of reference steel AISI52100 having a surface roughness (Ra) of 50 nm;

the plane is a plane flat mechanical part chosen from:

o PM1: a reference steel AISI52100; or

o PM2: made of APS steel plasma treated steel. PM1 has a surface roughness (Ra) of 50 nm.

PM2 has a surface roughness (Ra) of between 170 and 200 nm.

The conditions of the alternative triometer ball-plane test are:

- Temperature: 100 ° C

- Frequency: 5 Hz

Maximum contact pressure: 700 MPa

- Trace length: 5 mm

Duration: 1 h

- Volume of lubricating composition: 2-3 mL

The coefficients of friction and the wear of the balls in μηι in diameter of the impression of the ball indicated in Table 2 were measured following the contact of a smooth surface ball (Ra = 50 nm) with respectively a flat part PM1 smooth surface (Ra = 50 nm) or a flat surface PM2 rough surface (Ra = 170-200 nm), said parts are also in contact with a composition according to the invention or a comparative composition.

Table 2. Coefficients of friction and wear of the ball measured on an alternating ball-plane tribometer during the contacts between the ball and the pieces PM1 and PM2 respectively, the parts also being in contact with a composition according to the invention or a comparative composition

Nd: not determined These results demonstrate that:

The coefficient of friction between ball / PM1 is decreased when the lubricating composition comprises an organomolybdenum compound and titanium, regardless of the content of organomolybdenum compound and titanium. This coefficient of friction being measured between two pieces of smooth surface, it allows to determine the formation of MoS ₂ from the organomolybdenum compound. Nevertheless, the PM1 parts having smooth surfaces, the friction contacts are decreased relative to the friction contacts between a smooth surface piece and a rough surface piece such as PM2.

- The wear of the beads is lower when there is a combination between a composition according to the invention (CL1 or CL3) and the base oil in comparison with the base oil alone or with the comparative compositions (CC1, CC3 or CC4), for both types of surfaces (smooth or rough).

When the concentration of organomolybdenum compound is decreased (composition CL3), there is a more significant decrease in the coefficient of friction as well as the wear of the beads both with respect to the oil alone and compared to the comparative compositions.

The coefficient of friction between ball / PM2 (rough surface) is decreased when the lubricating composition comprises an organomolybdenum compound and titanium, regardless of the content of organomolybdenum compound and titanium.

That there is a synergy between the molybdenum and the titanium particles within the lubricant composition to significantly reduce the coefficient of friction and therefore to limit the friction between the parts.

Example 3 X-Ray Spectra

X-ray photoelectron spectroscopies were performed on the lubricant films (from compositions CL1 and CC3) obtained at the end of the tribological ball / PM1 tests.

Figure 1 shows the top spectrum of composition CC3 and bottom of composition CL1. This figure shows that in the absence of particles of Ti0 ₂ (CC3) decomposition of MoDTC is not complete and gives rise to the formation of MoS ₂ and MoOxSy Mo oxysulfide in large quantities. On the contrary, the presence of TiO ₂ allows a better decomposition of MoDTC and the formation of pure MoS ₂ .

Claims

1. Lubricating composition comprising:

at least one base oil;

from 0.05 to 1.5% by weight of an organomolybdenum compound; and

from 0.005 to 1% by weight of TiO ₂ particles.

2. - Composition according to claim 1, wherein the particles have an average size of between 10 nm and 1 μηι.

3. - Composition according to one of claims 1 or 2, comprising from 0.08 to 1% by weight of organomolybdenum compound relative to the total weight of said composition.

4. Composition according to any one of claims 1 to 3, comprising from 0.01 to 0.8% by weight of titanium particles relative to the total weight of said composition.

5. - Composition according to any one of claims 1 to 4, wherein the organomolybdenum compound is selected from organic complexes of molybdenum comprising at least one chemical molybdenum (Mo) and at least one ligand selected from carboxylate ligands, ester , amide, dithiophosphate or dithiocarbamate.

6. - Composition according to any one of claims 1 to 5, wherein the organomolybdenum compound is selected from organic complexes of molybdenum with amide ligands obtained by reaction:

(i) a mono, di or tri glyceride fatty substance, or fatty acid,

(ii) an amine source of formula (A):

in which :

X ¹ represents an oxygen atom or a nitrogen atom,

X ² represents an oxygen atom or a nitrogen atom,

n or m represents 1 when X ¹ or X ^{2 respectively} represents an oxygen atom,

n or m represents 2 when X ¹ or X ^{2 respectively} represents a nitrogen atom, (iii) and a molybdenum source selected from molybdenum trioxide or molybdates, preferably ammonium molybdate.

7. Composition according to any one of claims 1 to 5, wherein the organomolybdenum compound comprises at least one organic complex of molybdenum of formula (I I I) or (IV), alone or in melan e:

in which :

X ¹ represents an oxygen atom or a nitrogen atom;

X ² represents an oxygen atom or a nitrogen atom;

in which :

X ¹ represents an oxygen atom or a nitrogen atom;

X ² represents an oxygen atom or a nitrogen atom;

n represents 2 when X ¹ represents a nitrogen atom and m represents 2 when X ² represents a nitrogen atom; R 1 represents a linear or branched, saturated or unsaturated alkyl group comprising from 4 to 36 carbon atoms, preferentially from 4 to 20 carbon atoms, advantageously from 6 to 18 carbon atoms;

8. - Composition according to any one of claims 1 to 5, wherein the organomolybdenum compound is selected from organic complexes of molybdenum with dithiophosphate ligands or organic complexes of molybdenum with dithiocarbamate ligands.

9. - Composition according to any one of claims 1 to 5, wherein the organomolybdenum compound is a molybdenum dithiocarbamate compound (MoDTC).

10. - Use of the composition according to any one of claims 1 to 9 for the engine lubrication, including internal combustion engine, for example vehicle engine.

1 1 .- Use according to claim 10 to reduce friction.

12.- Use according to one of claims 9 or 10 to reduce the wear of engine parts.

13. A method for lubricating mechanical parts, in particular in an engine, in particular an internal combustion engine, comprising at least one step of contacting at least one part with a lubricant composition according to any one of claims 1 to 9. .